a) Field of the Invention
A process and a device are known from U.S. Pat. No. 5,321,501, wherein a scanning of an object, preferably an eye, is realized by means of a short-coherence light source and an interferometric beam path with an adjustable reflector in a reference beam path. This enables the detection of interferences or fringes between beam components which are reflected or scattered at layers of various depths and of light reflected in the reference beam path.
A problem consists in this arrangement in that a loss of resolution occurs due to the inevitable, because involuntary, eye movements of the subject, especially axial movements of the eye relative to the instrument, because individual scanned images change their position and can only be correlated with one another again through correlation calculations.
b) Description of the Related Art
In addition to the process and arrangement in the above patent, a scanning laser interferometer for fundus profile measurement was described by Drexler, Hitzenberger, Fercher, and Sattmann in "Conference on Holography and Interferometry in Biomedical Science", Budapest 1993, pages 1-9. Since this arrangement uses the interferences between the light reflected at the fundus and the light reflected at the cornea, axial eye movements are compensated for, but the different divergences of the reflected radiation brings about the problem of a poor signal-to-noise ratio.
Further, arrangements for intraocular distance measurement are also described in DE 3201801, U.S. Pat. No. 5,347,327, U.S. Pat. No. 5,347,328, DE 19624167 A1.
In DE 4446183 A1 by the present Applicant, at least one diffractive optical element (DOE) for dividing the illumination beam path into partial beam paths for different boundary surfaces or interfaces of the eye is provided for intraocular distance measurement, wherein this diffractive optical element is constructed as a type of phase Fresnel lens. The fabrication of micro-Fresnel lenses of this kind is described, for example, in APPLIED OPTICS, Vol. 28, No. 4, Feb. 15, 1989, pages 682-686, and Vol. 29, No. 34, Dec. 1, 1990, pages 5120-5126.